The retinal pigment epithelium (RPE) is a multifunctional and indispensable component of the vertebrate retina. The convoluted apical and basal plasma membranes of RPE cells provide a large surface area that allows rapid material exchange between these cells and their local microenvironment. The RPE is considered to be the primary lesion site of age-related macular degeneration (AMD), a disease that has pathology spanning the entire photoreceptor-RPE-choriocapillaris complex. The root cause of the initial damage to the RPE remains unclear. Because the RPE cells have an active transport role, we propose that a decline in membrane trafficking is sufficient to cause numerous adverse effects on membrane specialization, protein trafficking, and/or secretion. These effects could be conveyed to neighboring cells through direct cell-cell interaction and/or diffusion. Chloride intracellular channel 4 (CLIC4), an apical RPE protein, has an important role in vesicular exocytosis in other epithelial cell types. To study the physiological relevance of CLIC4, we have developed two novel rodent models in which CLIC4 can be selectively suppressed from RPE cells in situ (i.e., in vivo transfection, and conditional knockout mice). In both of these model systems, young adults manifest several cell autonomous and non-cell autonomous features that not only mirror each other, but also mimic the hallmarks of AMD. To build upon these findings, we will conduct a comprehensive characterization of these animals to better model the disease progression of AMD (Aim 1). Furthermore, we will directly test our model that the dysregulated vesicular trafficking function of CLIC4 is what causes the microvillar dysmorphogenesis and retinal detachment in the mutant animals (Aim 2). Finally, we will test the hypothesis that CLIC4 is important for the secretion of molecules produced by RPE cells (Aim 3). Imbalanced secretion may lead to atrophy in the adjacent tissues. Several innovative techniques, cell cultures, and state-of-the-art animal models will be used in combination to address these inter-related questions. These studies will enrich our fundamental understanding of the RPE and ultimately lead to better diagnosis of early AMD and rational design of treatments.